What actually regulates the lives of Roman Catholics is not so much old papal encyclicas as Canon law. The accusations against Freemasonry contained in Canon law are few and sweping. Canon 1374 of the new Code, promulgated in 1983, contains the clause used today. Interestingly, it does not mention Freemasonry by name:
A person who joins an association which plots against the Church is to be punished with a just penalty; one who promotes or takes office in such an association is to be punished with an interdict.
Thus, there is nothing in Canon law which forbids a Roman Catholic to become a Freemason. Not in so many words. To forestall any misinterpretation, Cardinal Ratzinger, the chief ideologist of the RCC, made an authoritative statement. He said that the fact that the "Masonic sect" is no longer explicitly named, as it was in the previous Canon Law from 1917, is irrelevant. The Church's negative judgment on Masonry remains unchanged. There has been a change of expression, not of content. Masonic associations are included under a more general heading which could include any other association conspiring against the Church.
The ban rests on the RCC hierarchy's interpretation of the Masonic movement. They claim that it is "plotting against the church". We have every reason to ask for evidence of such plotting. But this is not really available. I have searched high and low for it in Catholic sources without success. I found criticism against some historic Freemasonry and against a non-typical minority of rationalistic Freemasons. Even the people who wrote this criticism seem to realize that it is insufficient.
So why not give it up? No, that would threaten the credibility of those who made the first evaluation. The RCC hierarchy stick to it for that reason. To strengthen their arguments and still convince people that Freemasonry is wrong, they have added a number of different reasons which have nothing to do with what Canon Law actually says:
...even if the Masons did not plot against the church, it might be seriously wrong to join them for other reasons. The congregation presents as the reason for its judgment the fact that the principles of Masonry are "irreconcilable" with those of the church. The six-year study of Masonry by the German bishops and the study of American Masonry by Professor William Whalen (commissioned by the Pastoral Research and Practices Committee) both confirm that the principles and basic rituals of Masonry embody a naturalistic religion active participation in which is incompatible with Christian faith and practice.
So they recognize the possibility that Freemasonry may actually not be "plotting against the church". In that case, the ban is still valid because Freemasonry "embodies a naturalistic religion". Okay, so let us forget about the plotting and look at the alleged naturalism.